What's Cool In Road Cycling

Power Hour: Is There a Best Time of Day for a Breakthrough Performance?

Circadian rhythms affect many aspects of our physiology, from temperature to arousal and strength. Does it affect when our workout or racing ability might be optimal?

The body is not a static and stable entity, and chronobiology is one field of physiology that is often overlooked but which can be a major influence on both health and performance. We have all most likely heard of the term “circadian rhythm,” referring to cycles that occur over the course of a day (circadian = circa diem or ‘around a day’). Left in a room with no time cues, rhythms such as sleepiness, temperature, and levels of multiple hormones still revolve around a roughly 24 h cycle.

There are other time scales of physiological rhythms, including ultradian (scale of hours, such as feeding cycles) and infadian (beyond 24 h, such as the menstrual cycle).

These levels of hormones and rhythms can affect our exercise capacity over the course of a day. In today’s video Toolbox, we take a look at the question of whether there becomes an optimal time of the day to perform training or an optimal race effort.

Click Play to watch today’s Toolbox on video now…


Zadow EK, JW Fell, CM Kitic, J Han, SSX Wu. Effects of time of day on pacing in a 4-km time trial in trained cyclists. Int J Sports Physiol Perform. 15(10):1455-1459.

There is also an entire chapter about chronobiology and jet lag in my new 2nd Edition of Advanced Environmental Exercise Physiology.

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